Hydrant outlet Q

We had hydrant training last night and it made me wonder something... one of the teams instead of using the 4" output on the hydrant, used an adapter to hook the 4" supply line to a 2.5" discharge. What's the difference in flow between the 2... I argued that even with a 4" line, you're restriced by the 2.5 inch orifice of the hydrant... a bunch of the physics and engineer types thought it was neglible... I quickly shut up, but wondering if they're right?

What's the flow with a 2.5" hydrant output adapted to flow through 4" hose?
What's the flow with a 4" hydrant output to flow through 4" hose?

There are some real Numbers Guru's whom I suspect will be through shortly to answer your question, however from my foggy memory of Fluid Mechanics about 12 years ago - they are correct - the overall loss from the Discharge & adapter is negligible compared to the friction loss of the 4" hose.

Simple answer (I hope)

It appears that there is some confusion in the question at hand between friction loss and flow (GPM).

You are right. The 2.5" outlet converted will not provide the same GPM.

GPM is a function of opening diameter and velocity (pressure). To get the exact flow from each outlet of your hydrant you will need to test that specific hydrant. This can be done with a Pitot gauge (or any other flow testing gauge out there) and a flow chart. You should see that the larger opening flows more water.

A smaller diameter opening will not be able to provide the same amount of water as a larger opening at a given pressure. A chain is only as strong as its weakest link. Attaching a 4" hose will not increase GPM coming from the 2.5" outlet.

You are right that it will restrict flow, but the 2.5 port will still allow more than enough flow to allow the 4 inch to perform well (and far better than a 2.5 inch hose). Although it seems counterintuitive, both 4 inch hose, and a 2.5 inch steel port are capable of flowing up to 2000gpm with adequate pressure. The 4inch steel port alone can actually flow much, much, more than 2000gpm, but again, the 4 inch hose is the restriction.

Even on hydrant pressure, you still get much more than the flow capacity of 2.5 inch hose through the smaller port. The friction loss of 2.5 inch hose is significant, while the steel port has effectively no (or negligible) restriction other than the total volume limit.

The other advantages to using the 4 inch with adaptor are:

1. Consistency - For the small department that may put rookies on hydrant duty (like us), why advocate numerous scenarios and introduce possibility of mis-deployment of supply, when one hose size can be used in almost all scenarios.

2. Capacity - You will still flow more through one 2.5 port and 4 inch LDH, than 2x2.5 inch ports with a 2.5 inch hose on each.

3. Friction Loss - Regardless of what you are flowing, there is negligible friction loss in 4 inch, compared to moderate loss in 2.5 inch. You can flow up to 600gpm through 4inch before you get the same friction loss as 2.5 inch hose at 200gpm. You can get much longer lays out of it in any scenario.

And remember that you can flow the capacity of 4 inch hose out of a single 2.5 inch pump discharge too, so if you are relay pumping, you can use an adaptor directly into the big stuff to virtually eliminate friction loss and reduce the workload of the pump.

To find the max volume capacity of a steel discharge use this formula.

We had several long discussions on this topic about 6 months ago and I, and some others, ran some tests. Bottom line is LDH hooked to the steamer gets you the best flow obviously, but if the steamer is unavailable for whatever reason, LDH on a 2.5" is much, much better than 3". As stated the short length of restriction is quite significant but you can still get a lot of water through it.

Water system pressure has a lot to do with this. A water system that has 80 psi pressure on it is going to force a lot more water through that 2.5" into the LDH than a water system that has only 30. Even if the 30 psi system is capable of flowing 2000 GPM through the steamer port into LDH, it might not flow very good at all through the 2.5". The 80 psi system will do better in that case. Depends on if you have tanks on hills or water towers and pumps, etc.

OK, Where's The Spotted One??.............

Calling Dalmation90, report to the Hydraulics Debate!!.......

Dal has his act together on things like this, so when he comes along, you should get a scholarly answer. I can't add anything because we NEVER (Yes, I said Never) connect a Supply Line direct to a hydrant, There is ALWAYS (yes, I said always) an Engine on the hydrant to pump the line. We normally connect a 20'x6" Soft Sleeve to the hydrant, but if the 4.5 port is not useable, we put a section of 3 inch on BOTH 2.5 ports. I can usually get 1,000 GPM that way. Our hydrants range from 1,000-1,500 GPM up to 3,000 plus GPM, depending on the grid that the main is fed from. One hydrant that we use for drills runs 125 psi static, and drops to 90 psi at a flow of 2,000 GPM.

Whew... not sure if I'm more or less confused than before, but there sure is a LOT of good info here. In the scenario we were performing, they were using a 2.5" outlet on the hydrant adapted to 4" supply into a 4" steamer on the engine, and then pumping 2 3" supply lines to the attack engine.

My argument was we have the capability to use the 4" outlet on the hydrant, and that we should to get the most possible water out of it. It sounds from the above responses that I may be partially right? Our water supply guru (also a retired engineer) doesn't seem to agree.

At 14:00hrs something on Wednesday, during a gusty storm, I lost Cable TV / Internet to my home (and thus home office).

22:00hrs TV was restored, but apparently the parts to repair broadband were shipped on the slow boat from China. So I write this from a cafe, 48 hours after the outage began

The friction loss of an 2.5" outlet is negligible compared to the whole system. If I'm moving water, I'd much rather have a 4" on an 2.5" outlet, then a 2.5" hose on a 6" steamer outlet If I'm just filling a tank, I don't really care.

Let's look at the fundemental question:

"What's the difference in flow between the 2... "

The answer is...it depends.

First, it depends on the overall volume the hydrant can provide.

Second, it depends on the residual pressure while flowing that volume.

Let's take a hydrant that can provide 1500gpm @ 20psi residual pressure, which is the lowest the water departments like you running the residual.

Using the formula for solid bore nozzles, it takes an orifice 3.4" in diameter to deliver 1500gpm @ 20psi.

Indeed, at 20psi, a 2.5" will only flow about 850gpm.

NOW, something will happen between those two extremes -- almost all hydrants that can flow 1500gpm @ 20psi will increase their pressure as flow reduces. So that same hydrant may provide 1050gpm @ 30psi, which will deliver full volume through a 2.5" outlet. How various flows & associated residual pressures is affected is something you need to figure out based on your actual hydrants -- I know once you have several data points, there are calculations to estimate out the range of options, but I've never really played with them.

If we go on "We have really, really great residual pressure" systems, 1500gpm @ 60psi will flow that full volume through a 2.5" orifice.

Now also keep in mind the affects on the whole system during a major fire.

A system that can supply, say, 4500gpm @ 20psi will probably be able to deliver 1500gpm @ 60psi through a single 2.5" if that's the only hydrant in use. But as other hydrants are hit and your residual pressure goes down, the flow in that outlet will go down as residual drops below 60psi.

If you've developed SOPs based on a just using a single hydrant for an incident, you could have some head-scratching going on as master streams are screaming for water during a large incident.

Or that 1st due Engine that thought it had a small fire and just forward laid in a 3" line from a 2.5" outlet could find itself in a world of hurt as it's intake pressure keeps dropping as more and more hydrants are hit -- dropping the residual pressure that's needed to push a given volume through the hydrant's 2.5" outlet, then all that 3" hose.

So, hopefully I've made it clear as mud There's really no one, universal answer -- but it is a question that can be answered for any specific situation fairly easily if you know all the details.

I think the bottleneck in the above is the two 3" connections. While you will get more flow from the 4" discharge then the 2.5" discharge on the hydrant, both will flow more then your 2x3" will allow

You can move a hell of a lot of water through 2x3" after the pump, as the pump allows you to control the residual pressure and maintain maximum flow capacity. I am sure you will meet the capacity of even one big engine with that setup, assuming you are getting the volume into the first truck to begin with.

But having said that, a single 4" between the engines will flow the same amount with lower friction loss. Each inch of increased diameter in a given hose roughly doubles the flow, so a 4" hose flows twice as much as a three inch hose (or as much as two 3 inch hoses).

The downside to the 2x3" setup is each 3 inch hose has significantly more friction loss than the single 4", a longer lay of 3 inch will see the flow reduced more so than the same lay of 4 inch.

The downside to the 4 inch, is that it's operating pressure limit is usually around 175 psi, with a test max of 250 (higher pressure 4 & 5 inch is available). The 175 is not usually a problem unless you are pumping waaay uphill, or expect some water hammer from a sudden shutdown at the attack engine.

I also love working with 4 inch. Storz fittings, no way to get it backwards, and easy rinse and load after the fire. While I will still pull the small stuff for trash fires, etc. I would rather pull 4 inch over 2.5 or three inch any day. I know I have the flow I will need, and it is often quicker in the end.

Using the steamer will always give you the maximum flow for a particular layout (hydrant, pump, appliances, etc.)

HOWEVER

That is not necessarily the only correct answer.

In certain circumstances, you could be limited by other factors -- either on the hydrant side, or your layout (appliances, pumper, hose, etc) -- that means the maximum you will flow is still achievable through the 2.5" on the hydrant.

WHAT other factors we don't know is how your resident experts are deriving their opinions. If it's simply from a class taken 30 years ago, it might be suspect. If it's from that class...combined with years of experience with local operations and knowledge of how things work locally it could very well be true in a local situation you get the same flow in the same situation regardless of using the steamer or 2.5".

Perhaps the only true answer is wait until you're a company officer and can take the the truck and crew out for a drill and play with the flows yourself

I can also see situations in a drill where you might want to use a keystone valve* on a 2.5" discharge going to a 4". It's certainly easier / quicker to close and open the keystone then to close & open the hydrant itself -- so that might be an advantage if teaching or practicing on something that isn't really about hydrant operations.

============
* Keystone = 2.5" Gate Valve...since apparantly I come from one of the few fire departments in the world that calls a Keystone Valve a Keystone Valve

-- A Steamer to LDH adapter (we use 5" in my town...two different steamer threads though -- 4.5" and 6")

*and*

-- 2 Keystone valves

If we really want to suck the last 100gpm out of one of our hydrants (about 1500gpm max.) we will have a 5" suction to the steamer, and then run a 2.5" line from one the keystone valves to the auxiliary suction on our engine. After we're flowing water through the 5", the driver can connect the auxiliary, charge it, then slowly open the auxiliary suction to increase flow a tiny bit without shutting down.

Don't know what we'd do with the other 2.5" hydrant outlet since we're out of GPMs and PSIs at that point. Actually, I take that back slightly -- we do have one facility (a correctional center) whose yard hydrants are fed by a 3500gpm @ 120psi pump -- on those we could run a master stream directly off all three outlets on a hydrant

Around here a "fully dressed" or "big fire hook up" is both 2.5"'s and the steamer in use. We use both 2.5"s into short (10') 3" lines connected to a siamese into 5". The siamese is clappered to allow one side to be shut down and a pumper added in should the need to boost beyond hydrant pressure ever be needed. A neighboring department has a habit of gating only one 2.5 directly into a 5" line and this has caught them on a couple occasions that I'm aware of. Both of which we ended up laying a considerable amount of 5" as a secondary water supply.

We have found that 2-3" hoses into a clappered siamese into an LDH does not get you any more water than using a single 2.5" discharge with an immediate increase to the LDH. And it is a whole lot simpler and faster to hook up. Plus it leaves another discharge available for further use if the hydrant can support it.

I guess if you really wanted to "get the most out of your hydrant" you could hook a line to the steamer and one to one of the other ports. We're trying to do this more at my FT department. Although it's a 5" to the steamer and a gate valve and 3" to the side outlet, it's going to give more flow. I'd like to play with using an 2.5"x5" adapter, or even two sections of 3" siamesed into an additional 5" just to see how much flow we could get out of one.

We've even talked about doing like hwoods department and having an engine at the hydrant tandem pumping to the attack engine/truck to eliminate any FL between the hydrant and the scene.

Here's another way to look at the concept. Think of your siamese layout. Now eliminate one of the 3" hoses, i.e. hook one 2.5" siamese inlet directly to the hydrant. Now think about this for a minute. Do you think that other 50' of 3" hose around the back of the hydrant into the other port on the siamese is carrying much water? It's not. My suggestion is to further eliminate some restriction and use just a simple 2.5" to LDH increaser on the one side port of the hydrant, and put a gate on other side port for something else should the need arise.

I saw a photo in one of the magazines of someone doing just this. IIRC they had two LDH suctions, one into each side of an engine or quint, one off the steamer port and one off a side port. They were flowing on a warehouse fire or something. But the point is using the increaser is simple, effective, and it doesn't cost as much as a siamese appliance either.

I'd like to play with using an 2.5"x5" adapter, or even two sections of 3" siamesed into an additional 5" just to see how much flow we could get out of one.

I'm with Birk,

Skip the twin 3" all together, and just use your 2.5" to 4" (or 5") adapter.

That 3" in even a short 10' configuration is still hugely restrictive compared to the adapter only. You do not need to waste time with the second connection, other than to put on a gate valve for additional units to use.

First and foremost, with all other conditions being equal, a 4 hose connected to a 4 hydrant outlet will always (I am aware of the danger of using the word always) yield a greater flow rate than a 4 hose connected to a 2-½ hydrant outlet.

Having found some free time, I did some calculations to determine just how much greater the flow rate will be.

The 2 water supplies were used to check for a relatively good water supply and relatively poor water supply. Of course, some are better and some worse. Sorry, I am not going to try every possible water supply scenario.

Of note is that using both water supplies there is an approximate 54% to 58% increase in flow rate when using a 4 LDH connected to a 4 hydrant outlet versus 4 LDH connected to a 2-½ hydrant outlet. This holds for both water supplies. Whether or not this holds for other water supplies, I dont know. This, hopefully, answers the original question.

Oddly, the flow rate from two 3 hoses connected to the 2-½ outlets is greater than that of the 4 LDH connected to a 2-½ outlet.

Now, in doing the calculations I had to make some assumptions (which I held constant with each Option) and used pressure loss data for a particular hydrant. Other hydrants may change the specific values, but the comparative relationship should remain intact.

Finally, why is it that so few fire departments have hydrants with two 4 or 4-½ outlets? I know some do and they realize their worth.

City of Sacramento has a lot of dual steamers. They also have square operating nuts...? Anyway I think your assumption of dual 20' sections of 3" hose might be a tad unrealistic. Who carries 20' sticks of hose, and is that long enough to loop around the hydrant and any obstructions, into the siamese, without getting kinks? I think 50' sections would be more realistic.

Dual 3" lines aren't uncommon here, they'll couple any length that you want. Siamese and dual threes are strapped together along with a hydrant wrench as a hydrant pack. Pull the pack, wrap the hydrant and lay away. Here is an example of it in use.